Thrust reversal
Encyclopedia
Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine
's exhaust or changing of propeller pitch so that the thrust produced is directed forward, rather than aft. This acts against the forward travel of the aircraft, providing deceleration. Thrust reversers are used by many jet aircraft
to help slow down just after touch-down, reducing wear on the brakes and enabling shorter landing distances. It is also available on many propeller-driven aircraft
through reversing the controllable pitch propeller
s to a negative angle.
Reverse thrust is typically applied immediately after touchdown, often along with spoiler
s, to improve deceleration early in the landing roll when residual aerodynamic lift and high speed limit the effectiveness of the friction brakes located on the landing gear
. Reverse thrust is always selected manually, either using levers attached to the thrust lever
s or moving the thrust levers into a reverse thrust 'gate'. When thrust is reversed, passengers will hear a sudden increase in engine noise, in particular those seated just forward of the engines.
The early deceleration provided by reverse thrust can reduce landing roll by a third or more. Regulations dictate, however, that a plane must be able to land on a runway without the use of thrust reversers in order to be certified to land there as part of scheduled airline
service.
Once the aircraft's speed has slowed, thrust reverse is shut down to prevent the reversed airflow from raising debris in front of the engine intakes where it can be ingested, causing foreign object damage
. Thrust reverse is effective at any aircraft speed, and, if circumstances require, can be used all the way to a stop, or even to provide thrust to push the aircraft backward, though aircraft tug
s or towbars are more commonly used for that purpose. When reverse thrust is used to push an aircraft back from the gate, the maneuver is called a powerback
.
If the full power of reverse thrust is not desirable, thrust reverse can be operated with the throttles set at less than full power, even down to idle power, which reduces stress and wear on engine components. Reverse thrust is sometimes selected on idling engines to eliminate residual thrust, in particular in icy or slippery conditions, or where the engines' jet blast
could do damage.
For example, the ATR 72
turboprop can reverse thrust in flight, should the appropriate control lock be withdrawn. The Hawker Siddeley Trident
, a 120- to 180-seat airliner, was capable of descending at up to 10,000 ft/min (3,050 m/min) by use of the thrust reversers, though this capability was rarely used. Concorde
, too, could use reverse thrust in the air to increase the rate of descent. Only the inboard engines are used, and the engines are placed in reverse idle only when subsonic and below 30,000 ft. This will increase the rate of descent to around 10,000 fpm. The US Air Force's C-17A
is one of the few modern aircraft that uses reverse thrust in flight. The Boeing
-manufactured aircraft is capable of in-flight deployment of reverse thrust on all four engines to facilitate steep tactical descents up to 15,000 ft/min (4,600 m/min) into combat environments (this means that the aircraft's descent rate is just over 170 mph, or 274 km/h). The Saab 37 Viggen (retired in November 2005) also had the ability to use reverse thrust before landing, enabling the use of many roads constructed in Sweden to double as wartime runways.
The Shuttle Training Aircraft
, a highly modified Grumman Gulfstream II
, uses reverse thrust in flight to help simulate the Space Shuttle
aerodynamics so astronauts can practice landings.
and turboprop
aircraft can have reverse thrust, and almost all propeller aircraft with reverse thrust have the ability to set the propeller angle to flat pitch (called Beta range), which generates no forward or reverse thrust but provides large amounts of drag. This is especially useful in aircraft with complex reciprocating or turbine engines, as it enables engine speed to be kept high as the aircraft descends, avoiding doing damage to the engines by shock cooling
them.
aircraft generate reverse thrust by changing the angle of their controllable pitch propeller
s so that the propellers direct their thrust forward, instead of aft as normal. Reverse thrust has been available on propeller aircraft dating back to the 1930s. Reverse thrust became available due to the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions.
and Douglas DC-2
were among the first to feature reverse thrust. As piston aircraft became heavier and more complex, reverse thrust became more important to allow them to operate from airports originally configured to handle the smaller planes of previous years. In addition, the higher performance and greater altitude attainable by post-World War II
piston aircraft like the Lockheed Constellation
made the ability to use flat pitch, or, in extreme cases, reverse thrust, in order to descend and slow for landing without over-cooling the engines or approaching the runway with excessive speed. Finally, the advent of turboprops like the Vickers Viscount
and Lockheed Electra
brought even higher speeds and cruising altitudes to the fleet, as well as increased power
that could be used both for improved performance and to provide reverse thrust.
s and flying boat
s. These aircraft, when landing on water, have no conventional braking method and must rely on slaloming
and/or reverse thrust, as well as the drag
of the water in order to slow or stop. In addition, reverse thrust is often necessary for manoeuvring on the water, where it is used to make tight turns or even back the aircraft, such as when leaving a dock or beach.
s, thrust reversal is accomplished by causing the jet blast
to flow forward rather than aft. The engine does not run or rotate in reverse; instead, thrust reversers are used to block the blast and redirect it forward. Two methods are commonly used: In the target-type thrust reverser, the reverser blades angle outward, giving the general appearance of flower petals, and forcing engine thrust to flow forward. In the clamshell type, two reverser buckets are hinged so that when they deploy, they intrude into the exhaust of the engine, capturing and reorienting the jet blast. This type of reverser is usually clearly visible at the rear of the engine during use.
In addition to the two types used on turbojet and low-bypass turbofan engines, a third type of thrust reverser is found on some high-bypass turbofan engines. Doors in the bypass duct
are used to redirect the air that has been accelerated by the engine's fan section but has not passed through the combustion chamber (called bypass air) so that it provides reverse thrust.
The Boeing C-17 has a rare form of the above type in which even the exhaust from the core is redirected along with the main fan's air. This gives the C-17 unrivaled stopping ability among large jet-powered aircraft.
At least one accident is related to a small part of a thrust reverser, which had fallen off of another aircraft:
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
's exhaust or changing of propeller pitch so that the thrust produced is directed forward, rather than aft. This acts against the forward travel of the aircraft, providing deceleration. Thrust reversers are used by many jet aircraft
Jet aircraft
A jet aircraft is an aircraft propelled by jet engines. Jet aircraft generally fly much faster than propeller-powered aircraft and at higher altitudes – as high as . At these altitudes, jet engines achieve maximum efficiency over long distances. The engines in propeller-powered aircraft...
to help slow down just after touch-down, reducing wear on the brakes and enabling shorter landing distances. It is also available on many propeller-driven aircraft
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
through reversing the controllable pitch propeller
Controllable pitch propeller
A controllable pitch propeller or variable pitch propeller is a type of propeller with blades that can be rotated around their long axis to change their pitch...
s to a negative angle.
Operation
Spoiler (aeronautics)
In aeronautics, a spoiler is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly...
s, to improve deceleration early in the landing roll when residual aerodynamic lift and high speed limit the effectiveness of the friction brakes located on the landing gear
Landing Gear
Landing Gear is Devin the Dude's fifth studio album. It was released on October 7, 2008. It was his first studio album since signing with the label Razor & Tie. It features a high-profile guest appearance from Snoop Dogg. As of October 30, 2008, the album has sold 18,906 copies.-Track...
. Reverse thrust is always selected manually, either using levers attached to the thrust lever
Thrust lever
Thrust levers are found in the cockpit of aircraft, and are used by the pilot, copilot, or autopilot to control the power output of the aircraft's engines....
s or moving the thrust levers into a reverse thrust 'gate'. When thrust is reversed, passengers will hear a sudden increase in engine noise, in particular those seated just forward of the engines.
Airline
An airline provides air transport services for traveling passengers and freight. Airlines lease or own their aircraft with which to supply these services and may form partnerships or alliances with other airlines for mutual benefit...
service.
Once the aircraft's speed has slowed, thrust reverse is shut down to prevent the reversed airflow from raising debris in front of the engine intakes where it can be ingested, causing foreign object damage
Foreign object damage
Foreign Object Debris is a substance, debris or article alien to a vehicle or system which would potentially cause damage.Foreign Object Damage is any damage attributed to a foreign object that can be expressed in physical or economic terms that may or may not degrade the product's required...
. Thrust reverse is effective at any aircraft speed, and, if circumstances require, can be used all the way to a stop, or even to provide thrust to push the aircraft backward, though aircraft tug
Pushback
In aviation, pushback is an airport procedure during which an aircraft is pushed backwards away from an airport gate by external power. Pushbacks are carried out by special, low-profile vehicles called pushback tractors or tugs....
s or towbars are more commonly used for that purpose. When reverse thrust is used to push an aircraft back from the gate, the maneuver is called a powerback
Powerback
Powerback is used by aircraft to reverse using the power of their engines, In Europe only propeller aircraft tend to use powerbacks as a means of reversing, while in the USA some larger jet aircraft also perform powerbacks....
.
If the full power of reverse thrust is not desirable, thrust reverse can be operated with the throttles set at less than full power, even down to idle power, which reduces stress and wear on engine components. Reverse thrust is sometimes selected on idling engines to eliminate residual thrust, in particular in icy or slippery conditions, or where the engines' jet blast
Jet blast
Jet blast is the phenomenon of rapid air movement produced by the jet engines of aircraft, particularly on or before takeoff.A large jet-engined aircraft can produce winds of up to 100 mph up to 200 feet behind it at 40% maximum rated power...
could do damage.
In-flight operation
Some aircraft are able to safely use reverse thrust in flight, though the majority of these are propeller-driven. Many commercial aircraft cannot use reverse thrust in flight. Exceptions include Russian and Soviet aircraft that are able to reverse thrust in flight (mostly before touchdown). In-flight use of reverse thrust has several advantages: It allows for rapid deceleration, enabling quick changes of speed; it also prevents the speed buildup normally associated with steep dives, allowing for rapid loss of altitude, which can be especially useful in hostile environments such as combat zones, and when making steep approaches to land.For example, the ATR 72
ATR 72
The ATR 72 is a twin-engine turboprop short-haul regional airliner built by the French-Italian aircraft manufacturer ATR. ATR and Airbus are both built in Toulouse, and share resources and technology...
turboprop can reverse thrust in flight, should the appropriate control lock be withdrawn. The Hawker Siddeley Trident
Hawker Siddeley Trident
The Hawker Siddeley HS 121 Trident was a British short/medium-range three-engined jet airliner designed by de Havilland and built by Hawker Siddeley in the 1960s and 1970s...
, a 120- to 180-seat airliner, was capable of descending at up to 10,000 ft/min (3,050 m/min) by use of the thrust reversers, though this capability was rarely used. Concorde
Concorde
Aérospatiale-BAC Concorde was a turbojet-powered supersonic passenger airliner, a supersonic transport . It was a product of an Anglo-French government treaty, combining the manufacturing efforts of Aérospatiale and the British Aircraft Corporation...
, too, could use reverse thrust in the air to increase the rate of descent. Only the inboard engines are used, and the engines are placed in reverse idle only when subsonic and below 30,000 ft. This will increase the rate of descent to around 10,000 fpm. The US Air Force's C-17A
C-17 Globemaster III
The Boeing C-17 Globemaster III is a large military transport aircraft. Developed for the United States Air Force from the 1980s to the early 1990s by McDonnell Douglas, the C-17 is used for rapid strategic airlift of troops and cargo to main operating bases or forward operating bases throughout...
is one of the few modern aircraft that uses reverse thrust in flight. The Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
-manufactured aircraft is capable of in-flight deployment of reverse thrust on all four engines to facilitate steep tactical descents up to 15,000 ft/min (4,600 m/min) into combat environments (this means that the aircraft's descent rate is just over 170 mph, or 274 km/h). The Saab 37 Viggen (retired in November 2005) also had the ability to use reverse thrust before landing, enabling the use of many roads constructed in Sweden to double as wartime runways.
The Shuttle Training Aircraft
Shuttle Training Aircraft
The Shuttle Training Aircraft is a NASA training vehicle that duplicates the Space Shuttle's approach profile and handling qualities, allowing Space Shuttle pilots to simulate Shuttle landings under controlled conditions before attempting the task on board the orbiter.-Development:The aircraft's...
, a highly modified Grumman Gulfstream II
Grumman Gulfstream II
The Gulfstream II is an American twin engine business jet designed and built by Grumman and then in succession, Grumman American and finally Gulfstream American. Its Grumman model number is G-1159 and its US military designation is C-11 Gulfstream II. It has been succeeded by the Gulfstream III...
, uses reverse thrust in flight to help simulate the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
aerodynamics so astronauts can practice landings.
Types of aircraft
Small aircraft typically do not feature reverse thrust, except in specialized applications. On the other hand, large aircraft (weighing more than 12,500 lb) almost always have the ability to reverse thrust. Both reciprocating engineReciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...
and turboprop
Turboprop
A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...
aircraft can have reverse thrust, and almost all propeller aircraft with reverse thrust have the ability to set the propeller angle to flat pitch (called Beta range), which generates no forward or reverse thrust but provides large amounts of drag. This is especially useful in aircraft with complex reciprocating or turbine engines, as it enables engine speed to be kept high as the aircraft descends, avoiding doing damage to the engines by shock cooling
Shock cooling (engines)
Shock cooling refers to the theory that damage to engines may occur because of an excessively rapid decrease in temperature....
them.
Propeller-driven aircraft
Propeller-drivenPropeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
aircraft generate reverse thrust by changing the angle of their controllable pitch propeller
Controllable pitch propeller
A controllable pitch propeller or variable pitch propeller is a type of propeller with blades that can be rotated around their long axis to change their pitch...
s so that the propellers direct their thrust forward, instead of aft as normal. Reverse thrust has been available on propeller aircraft dating back to the 1930s. Reverse thrust became available due to the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions.
Multi-engine
Early multi-engine aircraft such as the Boeing 247Boeing 247
The Boeing Model 247 was an early United States airliner, considered the first such aircraft to fully incorporate advances such as all-metal semi-monocoque construction, a fully cantilevered wing and retractable landing gear...
and Douglas DC-2
Douglas DC-2
The Douglas DC-2 was a 14-seat, twin-engine airliner produced by the American company Douglas Aircraft Corporation starting in 1934. It competed with the Boeing 247...
were among the first to feature reverse thrust. As piston aircraft became heavier and more complex, reverse thrust became more important to allow them to operate from airports originally configured to handle the smaller planes of previous years. In addition, the higher performance and greater altitude attainable by post-World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
piston aircraft like the Lockheed Constellation
Lockheed Constellation
The Lockheed Constellation was a propeller-driven airliner powered by four 18-cylinder radial Wright R-3350 engines. It was built by Lockheed between 1943 and 1958 at its Burbank, California, USA, facility. A total of 856 aircraft were produced in numerous models, all distinguished by a...
made the ability to use flat pitch, or, in extreme cases, reverse thrust, in order to descend and slow for landing without over-cooling the engines or approaching the runway with excessive speed. Finally, the advent of turboprops like the Vickers Viscount
Vickers Viscount
The Vickers Viscount was a British medium-range turboprop airliner first flown in 1948 by Vickers-Armstrongs, making it the first such aircraft to enter service in the world...
and Lockheed Electra
Lockheed L-188 Electra
The Lockheed Model 188 Electra is an American turboprop airliner built by Lockheed. First flying in 1957, it was the first large turboprop airliner produced in the United States. Initial sales were good, but after two fatal crashes which prompted an expensive modification program to fix a design...
brought even higher speeds and cruising altitudes to the fleet, as well as increased power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
that could be used both for improved performance and to provide reverse thrust.
Single-engine
Single-engine aircraft tend to be of such limited size that the weight and complexity of reverse thrust is unwarranted. However, large single-engine aircraft like the Cessna Caravan & Pilatus Porter do have reverse thrust available, and single-engine seaplanes and flying boats tend to have reverse thrust as well. In other respects, reverse thrust on single-engine aircraft works much like that on other propeller aircraft.Seaplanes and flying boats
One special application of reverse thrust comes in its use on seaplaneSeaplane
A seaplane is a fixed-wing aircraft capable of taking off and landing on water. Seaplanes that can also take off and land on airfields are a subclass called amphibian aircraft...
s and flying boat
Flying boat
A flying boat is a fixed-winged seaplane with a hull, allowing it to land on water. It differs from a float plane as it uses a purpose-designed fuselage which can float, granting the aircraft buoyancy. Flying boats may be stabilized by under-wing floats or by wing-like projections from the fuselage...
s. These aircraft, when landing on water, have no conventional braking method and must rely on slaloming
Zigzag
A zigzag is a pattern made up of small corners at variable angles, though constant within the zigzag, tracing a path between two parallel lines; it can be described as both jagged and fairly regular....
and/or reverse thrust, as well as the drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
of the water in order to slow or stop. In addition, reverse thrust is often necessary for manoeuvring on the water, where it is used to make tight turns or even back the aircraft, such as when leaving a dock or beach.
Jet aircraft
On aircraft using jet engineJet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
s, thrust reversal is accomplished by causing the jet blast
Jet blast
Jet blast is the phenomenon of rapid air movement produced by the jet engines of aircraft, particularly on or before takeoff.A large jet-engined aircraft can produce winds of up to 100 mph up to 200 feet behind it at 40% maximum rated power...
to flow forward rather than aft. The engine does not run or rotate in reverse; instead, thrust reversers are used to block the blast and redirect it forward. Two methods are commonly used: In the target-type thrust reverser, the reverser blades angle outward, giving the general appearance of flower petals, and forcing engine thrust to flow forward. In the clamshell type, two reverser buckets are hinged so that when they deploy, they intrude into the exhaust of the engine, capturing and reorienting the jet blast. This type of reverser is usually clearly visible at the rear of the engine during use.
Turbofan
Bypass duct
A bypass duct is an annular passage that allows some of a turbofan's airflow to bypass the engine core, or gas generator. If the turbofan is unmixed, the bypass duct will terminate at the bypass nozzle...
are used to redirect the air that has been accelerated by the engine's fan section but has not passed through the combustion chamber (called bypass air) so that it provides reverse thrust.
The Boeing C-17 has a rare form of the above type in which even the exhaust from the core is redirected along with the main fan's air. This gives the C-17 unrivaled stopping ability among large jet-powered aircraft.
Thrust-reverse related accidents
In-flight deployment of thrust reversers has directly contributed to the crashes of several transport-type aircraft:- On 9 February 1982 Japan Airlines Flight 350Japan Airlines Flight 350Japan Airlines Flight 350 was a McDonnell Douglas DC-8-61, aircraft registration , on a domestic scheduled passenger flight from Fukuoka, Japan, to Tokyo. The airplane crashed 9 February 1982 on approach to Tokyo Haneda Airport in Tokyo Bay...
crashed 1000 feet (304.8 m) short of the runway at Tokyo Haneda AirportTokyo International Airport, commonly known as , is one of the two primary airports that serve the Greater Tokyo Area in Japan. It is located in Ōta, Tokyo, south of Tokyo Station....
following the intentional deployment of reverse thrust on two of the DC-8's four engines due to mental illness, resulting in 24 passenger deaths. - On August 29, 1990, a Lockheed C-5A crashed shortly after take-off from Ramstein Air BaseRamstein Air BaseRamstein Air Base is a United States Air Force base in the German state of Rheinland-Pfalz. It serves as headquarters for the United States Air Forces in Europe and is also a North Atlantic Treaty Organization installation...
in GermanyGermanyGermany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. As the aircraft started to climb off the runway, one of the thrust reversers suddenly deployed. This resulted in loss of control of the aircraft and the subsequent crash. Of the seventeen people on board, only four survived the crash. - On 26 May 1991 Lauda Air Flight NG004Lauda Air Flight 004Lauda Air Flight 004 was an international passenger flight that crashed due to a thrust reverser deployment of the number 1 engine in flight.-History of the flight:...
. The Boeing 767-300Boeing 767The Boeing 767 is a mid-size, wide-body twin-engine jet airliner built by Boeing Commercial Airplanes. It was the manufacturer's first wide-body twinjet and its first airliner with a two-crew glass cockpit. The aircraft features two turbofan engines, a supercritical wing, and a conventional tail...
aircraft suffered an uncommanded deployment of the No. 1 thrust reverser, which caused the airliner to stall and crash. All 213 passengers and 10 crew were killed. - On October 31, 1996, TAM Linhas Aéreas Flight 402. The Fokker 100 crashed shortly after take-off from Congonhas/São Paulo International Airport, São PauloSão PauloSão Paulo is the largest city in Brazil, the largest city in the southern hemisphere and South America, and the world's seventh largest city by population. The metropolis is anchor to the São Paulo metropolitan area, ranked as the second-most populous metropolitan area in the Americas and among...
, BrazilBrazilBrazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, striking an apartment building and several houses. All 90 passengers and 6 crew members on board died. Three people were killed on the ground. The crash was attributed to the uncommanded deployment of a faulty thrust-reverser on the right engine shortly after take-off.
At least one accident is related to a small part of a thrust reverser, which had fallen off of another aircraft:
- The Air France Concorde crashAir France Flight 4590Air France Flight 4590 was a Concorde flight operated by Air France which was scheduled to run from Charles de Gaulle International Airport near Paris, to John F. Kennedy International Airport in New York City. On 2000, it crashed in Gonesse, France. All one hundred passengers and nine crew...
of 2000 was attributed to a fragment of titanium that fell from the thrust reverser of a Continental AirlinesContinental AirlinesContinental Airlines was a major American airline now merged with United Airlines. On May 3, 2010, Continental Airlines, Inc. and UAL, Inc. announced a merger via a stock swap, and on October 1, 2010, the merger closed and UAL changed its name to United Continental Holdings, Inc...
DC-10 that had taken off some four minutes earlier. This fragment was traced to a third-party parts replacement that had not been approved by the FAA.